The invention relates to an apparatus for folding an airbag for a vehicle occupant restraint system, to a method of folding such an airbag as well as to a folded airbag.
Airbags that can be changed from a folded state into an unfolded state through the activation of a gas generator have meanwhile become a common feature of vehicle occupant restraint systems. An important requirement that such an airbag restraint system must fulfill is that the airbag has to be able to unfold completely within a very short period of time. The unfolding method is essentially determined by the manner in which the airbag was previously folded.
In the past, airbags were generally pleated in an accordion-like manner, for example, using folding blades. However, it was found that the relatively large folds created in this manner hinder the unfolding of the airbag. Nowadays, airbags are often not folded precisely, but rather simply pushed together, resulting in a chaotic folding pattern. The term xe2x80x9cchaoticxe2x80x9d means that the actual position of the various wall parts of the airbag cannot be predicted and will differ from one airbag to the next. In comparison to conventional methods that use folding blades, such a chaotic folding or pushing together method offers the advantage that it calls for less work for the folding and it results in better unfolding.
The object of the invention is to provide an apparatus as well as a method of folding an airbag in chaotic manner, with apparatus as well as method involving less effort for the folding.
This is achieved in an apparatus which comprises a base for the airbag to be folded, a cover for the airbag, and a flexible element that is arranged between the base and the cover and has first and second ends. The first end of the flexible element is held between the base and the cover. The apparatus further comprises a traction means that acts upon the second end of the flexible element, and a pressure generating means with which the airbag can be acted upon with compressed gas. The flexible element is arranged in such a way that it loops around the airbag which is disposed between the base and the cover. By pulling on the second end of the flexible element, the latter is pulled together, forming a loop that gets tighter and tighter. As a result, the airbag is pushed together from the outside towards the inside until it reaches the desired, completely folded state. In comparison to other apparatus that work with pushing elements or blades, this results in an especially simple structure, since no complicated movements are needed to fold the airbag; a simple pulling motion on the second end of the flexible element is sufficient.
Preferably, the base and the cover are arranged so as to have a defined distance from each other, the flexible element being a metal strip having a width which corresponds to this distance between the base and the cover. This forms a space that is completely enclosed by the metal strip, the base and the cover, and from which the airbag cannot escape when it is being folded. The metal strip is preferably a spring steel strip that, after being pulled together, recovers its original, expanded form once the second end is released.
According to the preferred embodiment of the invention, it is provided that the first end of the flexible element is firmly attached between the base and the cover. This facilitates both the mounting of the first end of the flexible element and the guidance of the flexible element in the area in which the flexible element is pulled out of the apparatus after it has encircled the airbag. After all, this is where the gap has to be as narrow as possible, so as to prevent the airbag from getting caught in the gap that is present between the flexible element forming the loop and the first end of the flexible element.
When the first end of the flexible element is affixed in the manner described, the entire airbag, except for the area that is immediately adjacent to the first end of the flexible element, is moved towards this first end while the airbag is being folded. For this reason, it is preferable for the base to be provided with a receptacle for a holding plate of the airbag and for the receptacle to be designed in the nature of a sliding guide. This ensures that the airbag, in spite of shifting when it is being pushed together, assumes a folded form in which its wall is arranged approximately symmetrically around the airbag""s inflation opening, which is normally located in the area of the holding plate.
According to an alternative embodiment, it can also be provided that the first end of the flexible element is disposed between the base and the cover in such a way that it can be translatorily shifted. With this configuration, the center of the airbagxe2x80x94that is to say, for example, the inflation opening that is provided with the holding platexe2x80x94remains stationary while all of the wall parts are moved symmetrically from the outside to the inside towards the inflation opening.
An adjusting cylinder, for instance, can be used to pull the flexible element out of the area between the base and the cover. Such an adjusting cylinder is a component of simple structure, with which the loop encircling the airbag can be pulled together easily, e.g. in a displacement-controlled or force-controlled manner. When the loop formed by the flexible element is pulled together in a displacement-controlled manner, the pushing procedure is only terminated once the airbag has been pushed together to a predefined circumference. When the airbag is pushed together in a force-controlled manner, the pulling together of the loop is completed as soon as the wall of the airbag offers a predefined resistance against being pushed together any further.
According to the preferred embodiment of the invention, the pressure generating means is configured as a fan. This makes it possible to pressurize the inside of the airbag in a simple manner so that the airbag unfolds between the base and the cover as well as the flexible element. In this manner, the airbag can be rendered into a partially folded state in which its height corresponds, for example, to the height of a receptacle provided to receive the airbag. In other words, the airbag is unfolded by the pressure generating means so as to have a shape in which the airbag has only a fraction of the height in comparison to the completely unfolded state.
In a preferred arrangement, the flexible element is provided with a large number of small openings and the pressure generating means is in flow connection with an outside surface of the flexible element. In this manner, an air cushion can be generated between the wall of the airbag and the flexible element. The air cushion reduces the friction between the wall of the airbag and the flexible element so that the flexible element entrains the walls not so much in the circumferential direction but rather acts upon them predominantly from the outside towards the inside.
In order to achieve the above-mentioned objective, a method of folding an airbag is also provided that comprises the following steps: first of all, the airbag is spread out on the base within an area that is encircled by the flexible element. Then the cover is placed onto the flexible element. Subsequently, the airbag is acted upon with pressure. As a result, it unfolds between the base, the cover and the flexible element. Then the flexible element is pulled together by pulling at its second end, as a result of which the airbag is pushed together. As far as the advantages of this method are concerned, reference is made to the explanations above.
An airbag that is folded together by the apparatus according to the invention and by the method according to the invention is distinguished in that its wall has a large number of chaotically arranged individual folding lines, several main folding lines being present that run in a slightly spiral shape around a center. The individual folding lines result from the essentially radial pushing together of the airbag from the outside towards the inside. The main folding lines that run in a spiral shape result from the friction between the flexible element and the walls of the airbag; the individual contact sites between the flexible element and the wall of the airbag execute a spiral-shaped motion when the loop formed around the airbag by the flexible element is pulled together.
Advantageous embodiments of the invention will be apparent from the subordinate claims.